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Full text of "The Cambridge Natural History"

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AQUATIC   Mammalia   of   fish-like   form;   tail   expanded   into
horizontal flukes; a fatty dor&ti " fin " present in most species;
anterior limbs converted Into fin-like paddles; posterior limbs
only represented by skeletal rudiments. Hairy covering re-
duced to a few isolated hairs in the neighbourhood of the
muzzle. Nostrils represented by the single or double blow-hole^
nearly always situated far back upon the skull. Bones of loose
texture and much impregnated with oiL The skull has a greatly-
developed facial portion ; supra-occipital bones meeting the frontal
by overgrowing, or growing in between the pariefcals; bones
surrounding the organ of hearing loosely attached to the skull,
the tympanics of peculiar cowrie-shell form. Coronoid process of
mandible absent, or very feebly developed. Teeth, when present,
few or numerous, always of simple conical form, with at most
traces of additional cusps (Inia); if absent their place taken by
whalebona Cervical vertebrae of short aBtero-posterior diameter,
often more or less completely welded together into a single mam.
Articulations between, dorsal and other vertebrae feeble. Scapula
peculiarly flattened; acromion strongly developed as a rule, but
arising from a slightly-marked spine; coracoid process generally
strongly developed. Phalanges of digits always more numerous
than in other mammals. Clavicles absent. Stomach complex,
consisting of at least four and often more chambers. Lungs
simple and non-lobulated. Diaphragm obliquely set and very
1 See Tan Benoden and Gervais, Ostt&graphie de$ (Maets ; and for a more general
t Beddaid, A Book tf WM^t lante, Jimmy,